Electromagnetic devices



March 29, 1960 F. E. ROMMEL ELECTROMAGNETIC DEVICES 2 Sheets-Sheet 1 Filed NOV. 1, 1956 Inventor E M ,5. WM

By a Attorney F. E. ROMMEL ELECTROMAGNETIC DEVICES March 29, 1960 2 Sheets-Sheet 2 Filed Nov. 1, 1956 l n ventor 7 4M 5. M M M l Afforne y is the same in the two cases,

ELECTROMAGNETIC DEVICES Frederick Emil Rommel, West Dulwich, London, England, assignor to Telephone Manufacturing Company Limited, London, England, a British company Application November 1, 1956, Serial No. 619,742

Claims priority, application Great Britain November 8, 1955 13 Claims. (Cl. 317-172) The invention relates to polarised electromagnetic relays and like polarised devices which have an armature arranged to be acted upon, through the magnetic structure of the device, by the variable operating flux produced by an input signal.

It is usual to employ a nickel-iron alloy, such as one of those known as Mumetal, as the material of the magnetic structure of such devices since these alloys are characterised by a small coercive force which ensures that little or no biasing effect is exerted on the armature by the resultant small residual flux, that is to say the flux remaining in the structure after an input signal stops. Such a biasing effect would, of course, be produced it the structure were madeof a material, such as siliconiron, having a comparatively large coercive force.

Unfortunately, however, not only are such nickel-iron alloys of extremely lowcoercive force much more expensive than silicon-iron, but also their saturation flux density (amounting to about 8,000 lines per sq. cm.) is low, being less than half that of silicon-iron. This imposes a limitation on the design of the devices magnetic structure since, in consequence its cross-section when made of such nickel-iron alloys must be at least twice that necessary when silicon-iron is employed, assuming of course that the total signal flux (which is determined by the desired sensitivity of the device) to be encountered This, of course, is particularly disadvantageous in devices where the space occupied by the magnetic structure and the signals winding is limited.

According to the present invention, in a polarised relay or like polarised device, the magnetic structure linked with the signals winding comprises a part through which the major portion of the operating flux flows and a second part shunting the first part and formed of a material which, compared with that of the first part, has a small coercive force, a small saturation flux density, and a large permeability at the magnetising force produced by residual flux in the first part, so that such residual flux is prevented from acting on the armature by being by-passed through the second part. Since'the magnetic structure of a device constructed according to the invention includes a part made of a material having a large saturation fiux density, it can carry a given signals flux with a smaller cross-sectional area than would be necessary if the structure were made wholly of a material having a small saturation flux density. On the other hand, the large coercive force'of the-first part does not bring about substantial biasing of the armature since the residual fiux in this first part is driven by this force, not through the armature, but through the second part against its small coercive force, this second part acting of course as a magnetic shunt of low reluctance because of its high permeability under these conditions.

Preferably the cross-sectional area of the first part is larger than that of the second part, so that then a magnetic structure of given cross-sectional area can carry a greater total flux.

" 2,930,946 Ce Patented Mar. 29,- 1960 The two materials used for the two parts are conveniently a usual grade of soft iron such as silicon-iron and a nickel-iron alloy of one of the types commercially known as Mumetal since these have the relevant properties mentioned above. Thus for example, their permeabilities at low magnetising forces such as 0.001 line per sq. cm. are 300 and 30,000 respectively.

In order to make the second part into the most efiicient shunt, the two parts are preferably arranged in contact with one another for the whole of their length so that the reluctance between them is small.

In order that the invention may be more easily understood and readily carried into effect two forms of relay constructed according to it will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic front view of the first form of relay;

Figure 2 is a cross-section of the first form of relay taken along the line IIII in Figure 1;

Figure 3 is a perspective view of a portion of the second form of relay; and

Figure 4 is an exploded perspective view of this second form of relay..

Referring first of all to Figures 1 and 2, the relay shown, which is of the Carpenter type inaccordance with US. PatentNo, 1,826,990, is provided with an armature 1 which is pivoted at 2 and which carries, at its upper end, the two moving contacts 3a and 3b which cooperate with stationary contacts 4a and 4b respectively. The pivot 2 of the armature lies in the air gap 5 between the two north pole faces of two permanent magnets 7a and 7b, the opposite poles of which are in direct contact with the upper ends of a magnetic structure 8. This structure 8 includes two pole pieces 8A and 8B, and is made up of three similarly shaped laminae 8a, 8b and (see Figure 2), with the lamina 8b arranged between and in direct contact with the other two laminae for all their length. The lower end of the armature 1 lies in the working air gap 10 situated between the faces of the pole-pieces 3A and 8B. The signals winding 11 of the relay is wound around the horizontal core SC of the magnetic structure.

In relays constructed hitherto in accordance with Figure 1, the structure 8 is made of a single material and this leads to one or other of the disadvantages already mentioned. Thus, if made of silicon-iron, the large coercive force of this material causes large residual fluxes to pass across the air gap 10 from one pole-piece to the other with resultant biasing of the armature.

In order to prevent or substantially reduce such biasing only two of the three laminae 8a, 8b, 80 making up the structure 8 with its pole pieces 8A, 8B are of silicon-iron, the third lamina, i.e. the central one 81; being of nickeliron alloy. Owing to this latter materials low coercive force and high permeability at magnetising fields of the order produced by the residual magnetism of the siliconiron laminae 8a and 8c, the flux (produced by this residual magnetism) which would otherwise cross the air gap 10 now proceeds from one pole face to the other through the lamina 8b. There is thus now no longer any field at the lower part of the armature so that the latter cannot become biased.

Referring now to Figures 3 and 4 of the second form of relay, which also has its magnetic circuit of the Car penter type, is constructed in accordance with US. Patent No. 2,559,399. The armature '20 of the relay is supported by two springs 21 which are secured by screws (one of which is shown at 22) to blocks 23 each of which is secured to one of the two main pole-pieces 24a and 24b of the frame. At its upper end the armature 20 carries the moving contacts (one of which is shown at 25) -which cooperate with two stationary contacts (not shown) lying on opposite sides of the armature. At its lower end, the armature lies between the two facing surfaces of the pole pieces 24a and 24b and it moves to and from these surfaces as the armature rocks.

The signals winding of the relay is carried by a horizontal laminated core 39 which is secured at each end-to a corresponding vertical laminated leg 31. Each of these legs 31 is at its upper end secured by screws 32 to one of the two pole-pieces 24a and 24b of the frame. Each of the permanent polarising magnets 33 (shown in dotted lines in Figure 3) of the relay is secured to a vertical silicon-iron shank 34 which is fixed to one of the pole-pieces 24a and 24b at 35. The shanks 34 serve to support the stationary contacts of the relay as described in the aforementioned specification. The two pole-pieces 24a and 245 are held in correct relationship with one another by screws (one of which is shown at 36) passing through both them and non-magnetic bushes 37.

So far, the construction of the relay is exactly the same as that described in the aforementioned specification. Thus the signals flux, which has a path similar to that in the relay shown in Figure 1, passes from the core up one leg 31, along one pole piece 241:, across the air gap between the members 24a and 24b (going through the lower end or" the armature) and then back to the core 3% through the pole piece 2% and the other leg 31. The polarising fiux produced by the magnets 33 passes down longitudinally of the armature Ztl, one portion of the flux returning to one magnet through the pole-piece 24a whilst the other portion returns to its magnet through the pole piece 241').

Hitherto, the pole-pieces 24a and 24b, the core 30 and the legs 31 have been made of silicon-iron, with consequent biasing of the armature as previously indicated. Such biasing is, of course, caused by the pole pieces 24:! and 241), the core 30 and the legs 31 acting as a single weak magnet whose poles are indicated at at and 41, the flux produced by this magnet traversing the air gap between the pole pieces 24a and 24b. In order to prevent, or substantially reduce this efiect the pole pieces 24:: and 24b, the core 3% and the legs 31 are made partly of siliconu'ron and partly (up to a half of the total crosssectional area) of the nickel-iron alloy known as Mumetal. Thus each of the pole pieces 24a and 24b is made up of tro laminae 24a, 24a" or 24b, 24b, the inner one (Zda', 24b) of which is of Mumetal, whilst the outer one, 24a, 24b" is of silicon-iron. At the same time, one of the three laminae making up each leg 31, and one of the three laminae making up the core 33 are of Mumetal whilst the remaining laminae are of silicon-iron. The Mumetal laminae are shown at 31' and 30 respectively. N w it can be seen from Figure 3 that the air gap between the pole-pieces 24a and 24b, is by-passed by the flux from the ends 40 and 411 this flux passing through the Mumetal laminae 24a, 24b, 30' and 31.

I claim:

1. In a polarized electromagnetic device of the kind comprising it signals winding, 21 core linked with said winding, a stationary magnetic structure including said core and defining a path for signals flux produced by a signal in said winding, an armature arranged to be acted upon by signals flux presented by said structure, and means providing polarizing fiux, said polarizing flux acting on said armature but substantially lay-passing said core, the novel feature that said structure comprises two parts connected magnetically in parallel with one another, the first of said parts carrying the major portion of the said signals flux and the second of said parts being formed of a material which, compared with that of the first of said parts has a small coercive force, a small saturation flux density, and a high permeability at the magnetizing force produced by residual fiux in the first of said parts, so that such residual flux is prevented from acting on said armature by being by-passed through the second of said parts.

2. A device according to claim 1, the second of said parts being of nickel-iron alloy.

3. A device according to claim 2, the first or" said parts being of silicon-iron.

4. A device according to claim 3, the cross-sectional area of the first of said parts being larger than the crosssectional area of the second of said parts.

5. A device according to claim 4, the two parts being in contact with one another for the whole of their length.

6. in a polarized electromagnetic device of the kind comprising a signals Winding, a core linked with said winding, a stationary magnetic structure including said core and defining a path for signals flux produced by a signal in said winding, said magnetic structure presenting a working air gap and comprising a plurality of laminae connected magnetically in parallel, an armature having a portion lying in said air gap arranged to be acted upon by signals flux presented by said structure, and means providing polarizing fiux, said polarizing flux acting on said armature but substantially by-passing said core, the novel feature that at least one or" said laminae being formed of one material while the others of said laminae are formed of a second material,-the second material, when compared with the first material, being of a small coercive force, a small saturation flux density, and a high permeability at the magnetizing force produced by residual link in the first material, whereby said residual flux is prevented from acting on said armature by being by-passed through said others of said laminae.

7. A device according to claim 6, the cross-sectional area of all the laminae of said first material being larger than the cross-sectional area of all the laminae of said second material.

8. A device according to claim 7, the first material being silicon-iron.

9. A device according to claim 8, the second material being a nickel-iron alloy.

10. In a polarized electromagnetic device of the kind comprising a signals winding, a core linked with said winding, a stationary magnetic structure including said core and defining a path for signals flux produced by a signal in said winding, said magnetic structure presenting a working air gap and comprising a plurality of portions arranged magnetically in series so that said signals tlux passes through said portions in series, an armature having a portion lying in said air gap arranged to be acted upon by signals flux presented by said structure, and means providing polarizing flux, said polarizing flux acting on said armature but substantially by-passing said core, the novel feature that each of said portions being formed with a plurality of laminae connected magnetically in parallel, at least one of said laminae of each portion being formed of a first material while the others of said laminae of each portion are formed of a second material, the second material, when compared with the first material, being of small coercive force, a small saturation flux density, and a high permeability at the magnetizing force produced by residual flux in the first material whereby said residual flux is prevented from acting on said armature by being by-passed through the laminae of said second material.

11. A device according to claim 10, wherein laminae of the second material define the said air gap.

12. A device according to claim 11, the said second material being a nickel-iron alloy.

13. A device according to claim 12, the said first mate rial being silicon-iron.

References Cited in the file of this patent UNITED STATES PATENTS 495,125 Stupakofi Apr. 11, 1893 1,826,990 Carpenter Oct. 13, 1931 2,559,399 Carpenter July 3, 1951 

